1. Field of the Invention
This invention relates to an image sensing apparatus using an image sensor such as a CCD or the like.
2. Description of the Related Art
When an image is picked up by an image sensing apparatus of the kind using an image sensor such as a CCD, a dark current generates a noise from within the image sensor in addition to an image signal generated according to the quantity of incident light. The level of the noise varies according to exposure time, temperature, etc. This noise is a serious cause for deterioration of images picked up. To solve this problem, the image sensor itself has been arranged to lower the dark current. Further, in the case of a still image camera having a shutter mechanism, the camera has been arranged to improve its S/N ratio by storing data of the dark current obtained when the shutter is closed and by subtracting the noise component of the dark current from the image signal obtained by shooting.
However, the conventional camera adapted for picking up motion images is not provided with any shutter mechanism for blocking light. Therefore, it has been hardly possible to improve the S/N ratio of the camera of this kind, because a noise component generated from within the image sensor cannot be detected. Besides, it has been hardly possible to separately take out the noise component because a motion image pickup operation cannot be allowed to have even a momentary pause for this purpose.